Cycle renders in gray (no color)
First of all: using CPU or GPU would not make any difference on the characteristics of the rendered image, other than rendering faster or slower.

I see three possible reasons why you have a black and white image:


You set up materials in blender internal and didn't create materials for cycles.

When no materials are present cycles will render everything with the default material, which is gray.


Cycles and Blender internal's materials are not compatible or interchangeable. you need to create new ones them using material nodes.


Maybe you did set materials but you set the output to render as B&amp;W. Set it to RGB or RGBA (Red, Green, Blue, Alpha)


Maybe you did set the materials correctly and the output to RGB (or RGBA),
but you set the render layer to use only one material, overriding all of the other materials for the scene: